Dd3 is starting to show interest in spelling, sometimes she'll say letter names, sometimes she'll write out a few letters to try for a word, sometimes she'll spell something out with the letter sounds. It's interesting to see her working through this.
Ds9 became interested in spelling when he realized he was really really good at it - he sometimes asks me to ask him a few big words, just for fun. This started around age 6. Still spelling on a spelling test is always much better than when he is just writing off the top of his head - I think this is probably common.
